Seat belt retractors are in common use on motor vehicles, the usual seat belt retractor sensor comprising means which will give a proportionate increase in pressure upon increase in acceleration or deceleration forces, and this pressure will urge a pawl into engagement with a toothed wheel on the seat belt retractor. Once the toothed wheel has been arrested in this rotation, this in turn functions to operate a secondary pawl which will prevent rotation of the seat belt retractor spool, thereby restraining the belt against feeding out, for example in the case of an accident which is associated with sudden acceleration forces.
However one of the difficulties encountered with this type of arrangement (which is the most commonly used arrangement) is that there can be a relatively slow movement of the pawl, or the development of a force which is not quite enough to urge the pawl into full engagement, and when only partial engagement of the pawl with the tips of the teeth of the toothed wheel occurs, it can result in damage to the pawl or to the toothed wheel. Furthermore, although the possibility is very slight, there is nevertheless the possibility of malfunction of the locking mechanism for the seat belt retractor.
One object of this invention is to provide improvements wherein this difficulty is substantially avoided, and a "snap action" is achieved.
This difficulty has been recognised previously, and in an acceleration sensor which was previously produced by the Applicant herein, a driver was provided with a centre of gravity located above pivot means so that it tended to topple, the driver having a peripheral lifting surface engaged by the periphery of an inverted cup-like yoke. However, in that invention the yoke had an upstanding stem guided for movement by the walls of an aperture in a tab on the seat belt retractor frame, and the employment of rubbing surfaces at that location made it necessary for the driver to have considerable mass, and therefore be of considerable size.
The main object of this invention is to provide improvements whereby there can be provided a variety of installation angles by the change of a small number of parts.